Qualcomm Snapdragon 439 Advantages
More modern manufacturing process (12nm vs 14nm)
Released 1 years and 1 months late
Qualcomm Snapdragon 660 Advantages
Better graphics card performance FLOPS (0.2176 TFLOPS vs 0.0432 TFLOPS )
Larger memory bandwidth (13.9GB/s vs 6.4GB/s)
Higher Frequency (2200MHz vs 2000MHz)